The catalytic and allosteric mechanism of regulatory enzymes will be investigated by equilibrium kinetics measured by isotopic exchange of substrates in a continuation of the study of the application of equilibrium kinetics to investigation of enzyme modifier action and allosteric enzyme action which originated and has been developed in this laboratory. Further theoretical development will be done on the elucidation of enzyme modifier action and regulatory ezyme mechanism by study of effects on equilibrium rates. The blood pressure regulatory enzyme, angiotensin coverting enzyme will be investigated in terms of structure and function.